The present application is based on and claims priority from Japanese Patent Applications: Hei 11-311190, filed Nov. 1, 1999; and 2000-24724, filed Jan. 28, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotation-angle-detection device for detecting an object to be detected by a magnetic sensor and a permanent magnet.
2. Description of the Related Art
In an electronically controlled throttle system, a rotary shaft of throttle valve is rotatably supported by an aluminum throttle body. The throttle valve is rotated by a rotary shaft, which is rotated by a motor, mounted on the throttle body, via a speed reduction unit. The rotary shaft is linked with a rotation-angle-detection device. The rotation-angle-detection device includes a rotor core, a permanent magnet that is fixed to the inner periphery of the rotor core, and a stator core. The stator core is molded into a resinous cover that covers an opening portion of the throttle body. The stator core is disposed inside rotor core to be coaxial therewith so that the inner periphery of permanent magnet is opposed to the outer periphery of stator core. A magnetic detection gap is formed in the stator core to penetrate the same in a radial direction to hold a Hall IC therein.
When magnetic flux of permanent magnet passes the stator core and the magnetic gap, the output signal of the Hall IC changes as the flux density changes. Because the flux density of the flux passing the magnetic detection gap changes as the permanent magnet rotates, it is possible to detect the rotation angle of permanent magnet by the Hall IC, and, in turn, the rotation angle (throttle open angle) of the throttle valve.
The cover extends longer in the longitudinal direction than the lateral direction so as to cover the motor and the speed reduction unit, and, accordingly, the resinous cover has a much larger thermal expansion coefficient than the metal-made throttle body. In addition, the detection direction of the Hall IC and the longitudinal direction of cover are parallel to each other.
If the cover thermally deforms, the magnetic detection gap and an air gap between stator core and permanent magnet changes, and the flux density of the flux passing the magnetic detection gap changes. As a result, the output voltage of the Hall IC may change and can not detect the rotation angle at a high accuracy.
Conventionally, an output error due to the temperature characteristics of a magnetic sensor is corrected by a temperature compensation element. However, it is very difficult to correct such an output error completely because of variation in characteristics of the magnetic sensors and the temperature compensation elements.
Further, if the resinous cover is made of a mere resinous mold, the resinous cover may warp or deform while throttle position sensor is put into use or manufactured. As a result, the Hall element and permanent magnet, which are disposed at resinous cover, may shift from each other, and the open angle of the throttle valve can not be detected accurately.
Therefore, an object of the invention is to provide a rotation-angle-detection device that can reduce fluctuation of the output signal of the magnetic sensor due to thermal deformation thereof, thereby improving the accuracy of the rotation position of an object to be detected.
According to an aspect of the invention, magnetic sensor is disposed so that the magnet-detecting direction and the longitudinal direction of the cover cross each other at a right angle. Therefore, the detection direction of the magnetic sensor is the same direction as the shorter side direction of the cover so that the distance change in the detection direction due to the thermal deformation of the cover can be reduced.
This reduces the change in the flux density in the detection direction, and the fluctuation of the output signal due to thermal deformation of the cover can be reduced. As a result, the detection accuracy of the rotation angle can be improved.
According to another aspect of the invention, a permanent magnet is fixed to a cylindrical rotor core rotating in response to the object to be detected. A stator core is disposed inside the rotor core to be coaxial therewith and is molded into the resinous cover. The magnetic sensor is fixed to a magnetic detection gap formed in the stator core to penetrate the stator core in a radial direction.
It is preferable that the detection direction of the magnetic sensor crosses the longitudinal direction of the cover at a right angle. In other words, the detection direction is in the same direction as the shorter side of the cover. Therefore, the change in size of the portion in the detection direction can be reduced, and the deformation of the magnetic detection gap, and the air gap between the stator core and the permanent magnet can be reduced.
In the meantime, the accuracy of the rotation-angle-detection device using a magnetic sensor is the best where the output signal of the magnetic sensor becomes zero. Because, the position where the output signal of the magnetic sensor becomes zero is the center of the straight portion of the output, which is excellent in linearity. In addition, the temperature does not affect the magnetic sensor at such a condition.
In view of the above characteristic, the permanent magnet and the magnetic sensor are disposed so that the output signal of the magnetic sensor becomes zero at an angle to be detected at a highest accuracy or its vicinity. Accordingly, the temperature influence on the magnetic sensor can be minimized in the rotation angle where a highest accuracy is required, so that the accuracy of the rotation angle can be improved.
The permanent magnet and the magnetic sensor can be disposed so that the output signal of the magnetic sensor becomes zero at a basic rotation angle, such as the position where the throttle valve is fully closed, of the object or its vicinity. Therefore, it is possible to minimize the influence of the temperature at a basic rotation angle of the object or its vicinity. Because the basic rotation angle can be detected at a high accuracy, it is possible to adjust the output signal of the magnetic sensor on the basis of the basic rotation angle, so that the accuracy of the rotation angle can be improved.
Another object of the invention is to provide an air intake control system in which a resinous mold having a simple structure made of heat-resistant reinforcing material is adopted so that the open angle of a throttle valve can be accurately detected.
According to another aspect of the invention, a heat resistant reinforcing member is provided to reinforce a resinous mold that accommodates a detecting element therein.
As a result, the resinous mold can be used under a high temperature condition without any problem, so that the detecting element can accurately detect the open angle of the throttle valve. In addition, the heat-resistant reinforcing member makes the resinous mold heat-resistant at a low cost.
The resinous mold may have a fixture member for fixing an external connection terminal for connecting the detecting element to the outside, and the heat-resistant reinforcing member is fixed to the fixture member in a unit. Therefore, heat problem of the fixture member can be prevented even if it is used under a high temperature condition.